Why This Population of Green Sea Turtles Is Turning All Female

Image: Mark Sullivan/NOAA

In one of the largest nesting grounds of green sea turtles in the world, researchers have uncovered a staggering statistic — over 99 percent of turtle hatchlings are being born female.

The problem? Warming sea and air temperatures caused by climate change.

Unlike mammals and other animals whose sex is influenced by chromosomes, the sex of sea turtle embryos is influenced by temperatures outside the egg. The optimal temperature for a mixed hatching of males and females is 85 degrees Fahrenheit. Just a few degrees lower, and the scales tip towards a predominantly male population, while temps just a few degrees higher lead to all female turtles.

Recently, researchers studied the green sea turtle population on Raine Island, located on the northern tip of the Great Barrier Reef — one of the largest breeding grounds for the turtles. Their analysis revealed that 99.1 percent of juveniles were female. Additionally, females made up 86.8 percent of the adult population.

Image: Brocken Inaglory, Wikimedia Commons

“Combining our results with temperature data show that the northern GBR green turtle rookeries have been producing primarily females for more than two decades and that the complete feminization of this population is possible in the near future,” write the authors of the study, which was published in Current Biology.

The research adds to growing concern about the effects of climate change on animals’ ability to thrive in their existing habitats. Because of green sea turtles’ temperature-dependent sex determination, warming temperatures could eventually be catastrophic to the population as males of breeding age die off and there are no new males to replace them.

“Our study highlights the need for immediate management strategies aimed at lowering incubation temperatures at key rookeries to boost the ability of local turtle populations to adapt to the changing environment and avoid a population collapse—or even extinction,” the paper warns.